Implantable pulse generator for providing functional and/or therapeutic stimulation of muscles and/or nerves and/or central nervous system tissue

ABSTRACT

Improved assemblies, systems, and methods provide an implantable pulse generator for prosthetic or therapeutic stimulation of muscles, nerves, or central nervous system tissue, or any combination. The implantable pulse generator is sized and configured to be implanted subcutaneous a tissue region. The implantable pulse generator includes an electrically conductive case of a laser welded titanium material. Control circuitry is located within the case, the control circuitry including a rechargeable power source, a receive coil for receiving an RF magnetic field to recharge the power source, and a microcontroller for control of the implantable pulse generator. Improved assemblies, systems, and methods also provide a stimulation system for prosthetic or therapeutic stimulation of muscles, nerves, or central nervous system tissue, or any combination. The stimulation system provides at least one electrically conductive surface, a lead connected to the electrically conductive surface, and an implantable pulse generator electrically connected to the lead.

RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.11/150,418, filed 10 Jun. 2005, and entitled “Implantable PulseGenerator for Providing Functional and/or Therapeutic Stimulation ofMuscles and/or Nerves and/or Central Nervous System Tissue,” which isincorporated herein by reference.

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 60/578,742, filed Jun. 10, 2004, and entitled“Systems and Methods for Bilateral Stimulation of Left and RightBranches of the Dorsal Genital Nerves to Treat Dysfunctions, Such asUrinary Incontinence” and U.S. Provisional Patent Application Ser. No.60/599,193, filed Aug. 5, 2004, and entitled “Implantable PulseGenerator for Providing Functional and/or Therapeutic Stimulation ofMuscles and/or Nerves” and U.S. Provisional Patent Application Ser. No.60/680,598, filed May 13, 2005, and entitled “Implantable PulseGenerator for Providing Functional and/or Therapeutic Stimulation ofMuscles and/or Nerves and/or Central Nervous System Tissue,” which areincorporated herein by reference.

FIELD OF INVENTION

This invention relates to systems and methods for providing stimulationof central nervous system tissue, muscles, or nerves, or combinationsthereof.

BACKGROUND OF THE INVENTION

Neuromuscular stimulation (the electrical excitation of nerves and/ormuscle to directly elicit the contraction of muscles) andneuromodulation stimulation (the electrical excitation of nerves, oftenafferent nerves, to indirectly affect the stability or performance of aphysiological system) and brain stimulation (the stimulation of cerebralor other central nervous system tissue) can provide functional and/ortherapeutic outcomes. While existing systems and methods can provideremarkable benefits to individuals requiring neuromuscular orneuromodulation stimulation, many limitations and issues still remain.For example, existing systems often can perform only a single, dedicatedstimulation function.

A variety of products and treatment methods are available forneuromuscular stimulation and neuromodulation stimulation. As anexample, neuromodulation stimulation has been used for the treatment ofurinary incontinence. Urinary incontinence is a lower pelvic regiondisorder and can be described as a failure to hold urine in the bladderunder normal conditions of pressure and filling. The most common formsof the disorder can arise from either a failure of muscles around thebladder neck and urethra to maintain closure of the urinary outlet(stress incontinence) or from abnormally heightened commands from thespinal cord to the bladder that produce unanticipated bladdercontractions (urge incontinence).

There exists both external and implantable devices for the purpose ofneuromodulation stimulation for the treatment of urinary urgeincontinence. The operation of these devices typically includes the useof an electrode placed either on the external surface of the skin, avaginal or anal electrode, or a surgically implanted electrode. Althoughthese modalities have shown the ability to provide a neuromodulationstimulation with positive effects, they have received limited acceptanceby patients because of their limitations of portability, limitations oftreatment regimes, and limitations of ease of use and user control.

Implantable devices have provided an improvement in the portability ofneuromodulation stimulation devices, but there remains the need forcontinued improvement. Implantable stimulators described in the art haveadditional limitations in that they are challenging to surgicallyimplant because they are relatively large; they require direct skincontact for programming and for turning on and off. In addition, currentimplantable stimulators are expensive, owing in part to their limitedscope of usage.

These implantable devices are also limited in their ability to providesufficient power which limits their use in a wide range of neuromuscularstimulation, and limits their acceptance by patients because of afrequent need to recharge a power supply and to surgically replace thedevice when batteries fail.

More recently, small, implantable microstimulators have been introducedthat can be injected into soft tissues through a cannula or needle.Although these small implantable stimulation devices have a reducedphysical size, their application to a wide range of neuromuscularstimulation application is limited. Their micro size extremely limitstheir ability to maintain adequate stimulation strength for an extendedperiod without the need for frequent recharging of their internal powersupply (battery). Additionally, their very small size limits the tissuevolumes through which stimulus currents can flow at a charge densityadequate to elicit neural excitation. This, in turn, limits or excludesmany applications.

It is time that systems and methods for providing neuromuscularstimulation address not only specific prosthetic or therapeuticobjections, but also address the quality of life of the individualrequiring neuromuscular and neuromodulation stimulation.

SUMMARY OF THE INVENTION

The invention provides improved assemblies, systems, and methods forproviding prosthetic or therapeutic stimulation of central nervoussystem tissue, muscles, or nerves, or muscles and nerves.

One aspect of the invention provides a stimulation assembly sized andconfigured to provide prosthetic or therapeutic stimulation of centralnervous system tissue, muscles, or nerves, or muscles and nerves. Thestimulation assembly includes an implantable pulse generator (IPG)attached to at least one lead and one electrode. The implantable pulsegenerator is implanted subcutaneously in tissue, preferably in asubcutaneous pocket located remote from the electrode. The electrode isimplanted in electrical conductive contact (i.e., the electrodeproximity to the excitable tissue allows current flow from the electrodeto excite the tissue/nerve) with at least one functional grouping ofneural tissue, muscle, or at least one nerve, or at least one muscle andnerve. The lead is tunneled subcutaneously in order to electricallyconnect the implantable pulse generator to the electrode.

Another aspect of the invention provides improved assemblies, systems,and methods for providing a universal device which can be used for manyspecific clinical indications requiring the application of pulse trainsto muscle and/or nervous tissue for therapeutic (treatment) orfunctional restoration purposes. Most of the components of theimplantable pulse generator are desirably sized and configured so thatthey can accommodate several different indications, with no or onlyminor change or modification. Technical features of the implantablepulse generator device include a secondary power source and/or primarypower source for improved service life, wireless telemetry forprogramming and interrogation, a single or limited number of stimulusoutput stage(s) for pulse generation that are directed to one or moreoutput channels, a lead connection header to provide reliable and easyconnection and replacement of the lead/electrode, a programmablemicrocontroller for timing and control of the implantable pulsegenerator device functions, and power management circuitry for efficientrecharging of the secondary power source and the distribution ofappropriate voltages and currents to other circuitry, all of which areincorporated within a small composite case for improved quality of lifeand ease of implantation.

In one embodiment, the implantable pulse generator comprises anelectrically conductive case, and includes a header that carries aplug-in receptacle(s) for attachment of a lead(s) and an antenna fortransmission and reception of wireless telemetry signals. Within thecase is located a circuit that generates electrical stimulationwaveforms, a rechargeable battery, including recharging circuitry, awireless telemetry circuit, and a programmable microcontroller whichcarries embedded code.

In one embodiment, an implantable pulse generator includes improvedpower management circuitry and operating modes for extended servicelife. The power management circuitry is generally responsible forrecovery of power from an RF magnetic field applied externally over theimplantable pulse generator, for charging and monitoring therechargeable battery, and for the distribution of appropriate voltagesand currents to other circuitry in the implantable pulse generator. Thepower management circuitry (through the use of logic and algorithmsimplemented by the microcontroller) communicates with an implantablepulse generator charger outside the body through the wireless telemetrycommunications link. The efficient recharging of the secondary powersource (rechargeable battery) is accomplished by adjusting the strengthof the RF magnetic field generated by the externally mounted implantablepulse generator charger in response to the magnitude of the voltagerecovered by the implantable pulse generator and the power demands ofthe implantable pulse generator's battery. The power management mayinclude operating modes configured to operate the implantable pulsegenerator at its most efficient power consumption throughout the storageand operation of the implantable pulse generator. These modesselectively disable or shut down circuit functions that are not needed.The modes may include, but are not limited to IPG Active and Charging,IPG Active, and IPG Dormant.

In one embodiment, an implantable pulse generator incorporates wirelesstelemetry. Wireless telemetry allows the implantable pulse generator towirelessly interact with a clinician programmer, a clinician programmerderivative, a patient controller, and an implantable pulse generatorcharger, for example. The wireless telemetry allows a clinician totransmit stimulus parameters, regimes, and other setting to theimplantable pulse generator before or after it has been implanted. Thewireless telemetry also allows the clinician to retrieve informationstored in the implantable pulse generator about the patient's usage ofthe implantable pulse generator and information about any modificationsto the settings of the implantable pulse generator made by the patient.The wireless telemetry also allows the patient controller operated bythe user to control the implantable pulse generator, both stimulusparameters and settings in the context of a therapeutic application, orthe real-time stimulus commands in the case of a neural prostheticapplication. In addition, the wireless telemetry allows the implantablepulse generator to communicate with the recharger (implantable pulsegenerator charger) during a battery recharge in order to adjust therecharging parameters if necessary, which provides for an efficient andeffective recharge. In addition, the wireless telemetry allows theoperating program of the implantable pulse generator, i.e., the embeddedexecutable code which incorporates the algorithms and logic for theoperation of the implantable pulse generator, to be installed or revisedafter the implantable pulse generator has been assembled, tested,sterilized, and perhaps implanted. This feature could be used to provideflexibility to the manufacturer in the factory and perhaps to arepresentative of the manufacturer in the clinical setting.

In one embodiment, an implantable pulse generator provides a clinicianprogrammer incorporating technology based on industry-standard hand-heldcomputing platforms. The clinician programmer allows the clinician orphysician to set parameters in the implantable pulse generator (IPG)relating to the treatment of the approved indication. The clinicianprogrammer uses the wireless telemetry feature of the implantable pulsegenerator to bi-directionally communicate to the implantable pulsegenerator. In addition, additional features are contemplated based onthe ability of the clinician programmer to interact with industrystandard software and networks to provide a level of care that improvesthe quality of life of the patient and would otherwise be unavailable.Such features, using subsets of the clinician programmer software, mightinclude the ability of the clinician or physician to remotely monitorand adjust parameters using the Internet or other known or futuredeveloped networking schemes. A clinician programmer derivative (orperhaps a feature included in the implantable pulse generator charger)would connect to the patient's computer in their home through anindustry standard network such as the Universal Serial Bus (USB), wherein turn an applet downloaded from the clinician's server would containthe necessary code to establish a reliable transport level connectionbetween the implantable pulse generator and the clinician's clientsoftware, using the clinician programmer derivative as a bridge. Such aconnection may also be established through separately installedsoftware. The clinician or physician could then view relevant diagnosticinformation, such as the health of the unit or its current efficacy, andthen direct the patient to take the appropriate action. Such a featurewould save the clinician, the patient and the health care systemsubstantial time and money by reducing the number of office visitsduring the life of the implant.

Other features of the clinician programmer, based on an industrystandard platform, might include the ability to connect to theclinician's computer system in his or her office. Such features may takeadvantage of the Conduit connection employed by Palm OS® based devices.Such a connection then would transfer relevant patient data to the hostcomputer or server for electronic processing and archiving. With afeature as described here, the clinician programmer then becomes anintegral link in an electronic chain that provides better patientservice by reducing the amount of paperwork that the physician's officeneeds to process on each office visit. It also improves the reliabilityof the service since it reduces the chance of mis-entered or mis-placedinformation, such as the record of the parameter setting adjusted duringthe visit.

Other features and advantages of the inventions are set forth in thefollowing specification and attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view of a stimulation assembly that provides electricalstimulation to central nervous system tissue, muscles and/or nervesinside the body using a general purpose implantable pulse generator.

FIG. 2A is a front view of the general purpose implantable pulsegenerator shown in FIG. 1.

FIG. 2B is a side view of the general purpose implantable pulsegenerator shown in FIG. 2A.

FIG. 3 is a view showing how the geometry of the implantable pulsegenerator shown in FIGS. 2A and 2B aids in its implantation in a tissuepocket.

FIG. 4A is a view showing the implantable pulse generator shown in FIGS.2A and 2B in association with a transcutaneous implantable pulsegenerator charger (battery recharger) including an integral chargingcoil which generates the RF magnetic field, and also showing theimplantable pulse generator charger using wireless telemetry tocommunicate with the implantable pulse generator.

FIG. 4B is an anatomic view showing the transcutaneous implantable pulsegenerator charger (battery recharger) as shown in FIG. 4A, including aseparate, cable coupled charging coil which generates the RF magneticfield, and also showing the implantable pulse generator charger usingwireless telemetry to communicate with the implantable pulse generator.

FIG. 4C is a perspective view of the implantable pulse generator chargerof the type shown in FIGS. 4A and 4B, with the charger shown docked on arecharge base with the charging base connected to the power mains.

FIG. 5A is an anatomic view showing the implantable pulse generatorshown in FIGS. 2A and 2B in association with an external programmer thatrelies upon wireless telemetry, and showing the programmer's capabilityof communicating with the implantable pulse generator up to an arm'slength away from the implantable pulse generator.

FIG. 5B is a system view of an implantable pulse generator systemincorporating a clinician programmer derivative and showing the system'scapability of communicating and transferring data over a network,including a remote network.

FIG. 5C is a perspective view of one possible type of patient controllerthat may be used with the implantable pulse generator shown in FIGS. 2Aand 2B.

FIG. 6 is a block diagram of a circuit that the implantable pulsegenerator shown in FIGS. 2A and 2B can incorporate.

FIG. 7 is a circuit diagram showing a possible circuit for the wirelesstelemetry feature used with the implantable pulse generator shown inFIGS. 2A and 2B.

FIG. 8 is a circuit diagram showing a possible circuit for the stimulusoutput stage and output multiplexing features used with the implantablepulse generator shown in FIGS. 2A and 2B.

FIG. 9 is a graphical view of a desirable biphasic stimulus pulse outputof the implantable pulse generator for use with the system shown in FIG.1.

FIG. 10 is a circuit diagram showing a possible circuit for themicrocontroller used with the implantable pulse generator shown in FIGS.2A and 2B.

FIG. 11 is a circuit diagram showing one possible option for a powermanagement sub-circuit where the sub-circuit includes MOSFET isolationbetween the battery and charger circuit, the power managementsub-circuit being a part of the implantable pulse generator circuitshown in FIG. 6.

FIG. 12 is a circuit diagram showing a second possible option for apower management sub-circuit where the sub-circuit does not includeMOSFET isolation between the battery and charger circuit, the powermanagement sub-circuit being a part of the implantable pulse generatorcircuit shown in FIG. 6.

FIG. 13 is a circuit diagram showing a possible circuit for the VHHpower supply feature used with the implantable pulse generator shown inFIGS. 2A and 2B.

The invention may be embodied in several forms without departing fromits spirit or essential characteristics. The scope of the invention isdefined in the appended claims, rather than in the specific descriptionpreceding them. All embodiments that fall within the meaning and rangeof equivalency of the claims are therefore intended to be embraced bythe claims.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The various aspects of the invention will be described in connectionwith providing stimulation of central nervous system tissue, muscles, ornerves, or muscles and nerves for prosthetic or therapeutic purposes.That is because the features and advantages that arise due to theinvention are well suited to this purpose. Still, it should beappreciated that the various aspects of the invention can be applied toachieve other objectives as well.

I. Stimulation Assembly

A. System Overview

FIG. 1 shows an assembly 10 for stimulating a central nervous systemtissue, nerve, or a muscle, or a nerve and a muscle for therapeutic(treatment) or functional restoration purposes. The assembly includes animplantable lead 12 coupled to an implantable pulse generator or IPG 18.The lead 12 and the implantable pulse generator 18 are shown implantedwithin a tissue region T of a human or animal body.

The distal end of the lead 12 includes at least one electricallyconductive surface, which will in shorthand be called an electrode 16.The electrode 16 is implanted in electrical conductive contact with atleast one functional grouping of neural tissue, muscle, or at least onenerve, or at least one muscle and nerve. The implantable pulse generator18 includes a connection header 14 that desirably carries a plug-inreceptacle for the lead 12. In this way, the lead 12 electricallyconnects the electrode 16 to the implantable pulse generator 18.

The implantable pulse generator 18 is sized and configured to beimplanted subcutaneously in tissue, desirably in a subcutaneous pocketP, which can be remote from the electrode 16, as FIG. 1 shows.Desirably, the implantable pulse generator 18 is sized and configured tobe implanted using a minimally invasive surgical procedure.

The surgical procedure may be completed in a number of steps. Forexample, once a local anesthesia is established, the electrode 16 ispositioned at the target site. Next, a subcutaneous pocket P is made andsized to accept the implantable pulse generator 18. The pocket P isformed remote from the electrode 16. Having developed the subcutaneouspocket P for the implantable pulse generator 18, a subcutaneous tunnelis formed for connecting the lead 12 and electrode 16 to the implantablepulse generator 18. The lead 12 is routed through the subcutaneoustunnel to the pocket site P where the implantable pulse generator 18 isto be implanted. The lead 12 is then coupled to the implantable pulsegenerator 18, and both the lead 12 and implantable pulse generator 18are placed into the subcutaneous pocket, which is sutured closed.

As FIGS. 2A and 2B shows, the implantable pulse generator 18 includes acircuit 20 that generates electrical stimulation waveforms. An on-board,rechargeable battery 22 desirably provides the power. The implantablepulse generator 18 also desirably includes an on-board, programmablemicrocontroller 24, which carries embedded code. The code expressespre-programmed rules or algorithms under which the desired electricalstimulation waveforms are generated by the circuit 20. The implantablepulse generator 18 desirably includes an electrically conductive case26, which can also serve as the return electrode for the stimuluscurrent introduced by the lead/electrode when operated in a monopolarconfiguration.

According to its programmed rules, when switched on, the implantablepulse generator 18 generates prescribed stimulation waveforms throughthe lead 12 and to the electrode 16. These stimulation waveformsstimulate the central nervous system tissue, muscle, nerve, or bothnerve and muscle tissue that lay in electrical conductive contact (i.e.,within close proximity to the electrode surface where the currentdensities are high) with the electrode 16, in a manner that achieves thedesired therapeutic (treatment) or functional restoration result. Aspreviously discussed, urinary incontinence is just one example of afunctional restoration result. Additional examples of desirabletherapeutic (treatment) or functional restoration indications will bedescribed in greater detail in section II.

The assembly 10 may also include additional operative components, suchas but not limited to, a clinician programmer, a clinician programmerderivative, a patient controller, and an implantable pulse generatorcharger, each of which will be discussed later.

B. The Implantable Pulse Generator

Desirably, the size and configuration of the implantable pulse generator18 makes possible its use as a general purpose or universal device(i.e., creating a platform technology), which can be used for manyspecific clinical indications requiring the application of pulse trainsto central nervous system tissue, muscle and/or nervous tissue fortherapeutic (treatment) or functional restoration purposes. Most of thecomponents of the implantable pulse generator 18 are desirably sized andconfigured so that they can accommodate several different indications,without major change or modification. Examples of components thatdesirably remain unchanged for different indications include the case26, the battery 22, the power management circuitry 40 for recharging thebattery 22, the microcontroller 24, much of the software (firmware) ofthe embedded code, and the stimulus power supply. Thus, a new indicationmay require only changes to the programming of the microcontroller 24.Most desirably, the particular code is remotely embedded in themicrocontroller 24 after final assembly, packaging, and sterilization ofthe implantable pulse generator 18.

Certain components of the implantable pulse generator 18 may be expectedto change as the indication changes; for example, due to differences inleads and electrodes, the connection header 14 and associatedreceptacle(s) for the lead may be configured differently for differentindications. Other aspects of the circuit 20 may also be modified toaccommodate a different indication; for example, the stimulator outputstage(s), sensor(s) and/or sensor interface circuitry.

In this way, the implantable pulse generator 18 is well suited for usefor diverse indications. The implantable pulse generator 18 therebyaccommodates coupling to a lead 12 and an electrode 16 implanted indiverse tissue regions, which are targeted depending upon thetherapeutic (treatment) or functional restoration results desired. Theimplantable pulse generator 18 also accommodates coupling to a lead 12and an electrode 16 having diverse forms and configurations, againdepending upon the therapeutic or functional effects desired. For thisreason, the implantable pulse generator can be considered to be generalpurpose or “universal.”

1. Desirable Technical Features

The implantable pulse generator 18 can incorporate various technicalfeatures to enhance its universality.

a. Small, Composite Case

According to one desirable technical feature, the implantable pulsegenerator 18 can be sized small enough to be implanted (or replaced)with only local anesthesia. As FIGS. 2A and 2B show, the functionalelements of the implantable pulse generator 18 (e.g., circuit 20, themicrocontroller 24, the battery 22, and the connection header 14) areintegrated into a small, composite case 26. As FIGS. 2A and 2B show, thecase 26 defines a small cross section; e.g., (5 mm to 10 mm thick)×(15mm to 40 mm wide)×(40 mm to 60 mm long), and an overall weight ofapproximately 10 to 15 grams. These dimensions make possibleimplantation of the case 26 with a small incision; i.e., suitable forminimally invasive implantation. Additionally, a larger, but similarlyshaped implantable pulse generator might be required for applicationswith more stimulus channels (thus requiring a larger connection header)and or a larger internal battery.

The case 26 of the implantable pulse generator 18 is desirably shapedwith a smaller end 30 and a larger end 32. As FIG. 3 shows, thisgeometry allows the smaller end 30 of the case 26 to be placed into theskin pocket P first, with the larger end 32 being pushed in last.

Desirably, the case 26 for the implantable pulse generator 18 comprisesa laser welded titanium material. This construction offers highreliability with a low manufacturing cost. The clam shell constructionhas two stamped or successively drawn titanium case halves that arelaser welded around the circuit assembly and battery 22 with feed-thrus.Typically, a molded plastic spacing nest is used to hold the battery 22,the circuit 20, and perhaps a power recovery (receive) coil together andsecure them within the titanium case.

The implantable pulse generator 18 shown in FIGS. 2A and 2B includes aclam-shell case 26 having a thickness that is selected to provideadequate mechanical strength while balancing the greater powerabsorption and shielding effects to the low to medium frequency magneticfield 52 used to transcutaneously recharge the implantable pulsegenerator Lithium Ion battery 22 with thicker case material (thecompeting factors are poor transformer action at low frequencies—due tothe very low transfer impedances at low frequencies—and the highshielding losses at high frequencies). The selection of the thicknessensures that the titanium case allows adequate power coupling torecharge the secondary power source (described below) of the pulsegenerator 18 at the target implant depth using a low frequency radiofrequency (RF) magnetic field 52 from an implantable pulse generatorcharger 34 mounted on the skin. Preferably, the implantable pulsegenerator 18 is implanted at a target implant depth of not less thanfive millimeters beneath the skin, and not more than fifteen millimetersbeneath the skin, although this implant depth may change due to theparticular application, or the implant depth may change over time basedon physical conditions of the patient, for example.

b. Secondary Power Source

According to one desirable technical feature, the implantable pulsegenerator 18 desirably possesses an internal battery capacity sufficientto allow operation with recharging not more frequently than once perweek for many or most clinical applications. The battery 22 of theimplantable pulse generator 18 desirably can be recharged in less thanapproximately five hours with a recharging mechanism that allows thepatient to sleep in bed or carry on most normal daily activities whilerecharging the battery 22 of the implantable pulse generator 18.

To achieve this feature, the battery 22 of the implantable pulsegenerator 18 desirably comprises a secondary (rechargeable) powersource; most desirably a Lithium Ion battery 22. Given the averagequiescent operating current (estimated at 8 μA plus 35 μA for a wirelesstelemetry receiver pulsing on twice every second) and a seventy percentefficiency of the stimulus power supply, a 1.0 Amp-hr primary cellbattery can provide a service life of less than two years, which is tooshort to be clinically or commercially viable for this indication.Therefore, the implantable pulse generator 18 desirably incorporates asecondary battery 22 (a rechargeable battery), e.g., a Lithium Ionsecondary battery that can be recharged transcutaneously. Givenrepresentative desirable stimulation parameters (which will be describedlater), a Lithium Ion secondary battery with a capacity of at least 30mA-hr will operate for almost three weeks. Lithium Ion implant gradebatteries are available from a domestic supplier. A representativebattery provides 35 mA-hr in a package configuration that is ofappropriate size and shape to fit within the implantable pulse generator18. The implantable pulse generator 18 could also incorporate a smallprimary battery to provide current to prevent self-discharge of thesecondary battery 22 from dropping its voltage to the point ofirreversible damage to the secondary battery.

The power for recharging the battery 22 of the implantable pulsegenerator 18 is provided through the application of a low frequency(e.g., 30 KHz to 300 KHz) RF magnetic field 52 applied by a skin orclothing mounted recharger 34 placed over the implantable pulsegenerator (see FIGS. 4A and 4B). In one possible application, it isanticipated that the user would wear the recharger 34, including aninternal magnetic coupling coil (charging coil) 35, over the implantablepulse generator 18 to recharge the implantable pulse generator 18 (seeFIG. 4A). Alternatively, the recharger 34 might use a separate magneticcoupling coil (charging coil) 35 which is placed and/or secured on theskin or clothing over the implantable pulse generator 18 and connectedby cable to the recharger 34 (circuitry and battery in a housing) thatis worn on a belt or clipped to the clothing (see FIG. 4B).

The charging coil 35 preferably includes a predetermined construction,e.g., desirably 150 to 250 turns, and more desirably 200 turns of sixstrands of #36 enameled magnetic wire, or the like. Additionally, thecharging coil mean diameter is in a range of about 40 millimeters to 60millimeters, and desirably about 50 millimeters, although the diametermay vary. The thickness of the charging coil 35 as measuredperpendicular to the mounting plane is to be significantly less than thediameter, e.g., two to five millimeters, so as to allow the coil to beembedded or laminated in a sheet to facilitate placement on or near theskin. Such a construction will allow for efficient power transfer andwill allow the charging coil 35 to maintain a temperature below 41degrees Celsius.

The recharger 34 preferably includes its own internal batteries whichmay be recharged from the power mains, for example. A charging base 39may be included to provide for convenient docking and recharging of thesystem's operative components, including the recharger and therecharger's internal batteries (see FIG. 4C). The implantable pulsegenerator recharger 34 does not need to be plugged into the power mainswhile in use to recharge the implantable pulse generator.

Desirably, the implantable pulse generator 18 may be recharged while itis operating and will not increase in temperature by more than twodegrees Celsius above the surrounding tissue during the recharging. Itis desirable that the recharging of the battery 22 requires not morethan six hours, and a recharging would be required between once permonth to once per week depending upon the power requirements of thestimulus regime used.

The implantable pulse generator 18 desirably incorporates circuitryand/or programming to assure that the implantable pulse generator 18will suspend stimulation, and perhaps fall-back to only very low ratetelemetry, and eventually suspends all operations when the secondarybattery 22 has discharged the majority of it capacity (i.e., only asafety margin charge remains). Once in this dormant mode, theimplantable pulse generator can be restored to normal operation only byrecharging as shown in FIGS. 4A and 4B.

c. Wireless Telemetry

According to one desirable technical feature, the system or assembly 10includes an implantable pulse generator 18, which desirably incorporateswireless telemetry (rather that an inductively coupled telemetry) for avariety of functions to be performed within arm's reach of the patient,the functions including receipt of programming and clinical parametersand settings from the clinician programmer 36, communicating usagehistory to the clinician programmer, providing user control of theimplantable pulse generator 18, and for controlling the RF magneticfield 52 generated by the implantable pulse generator charger 34. Eachimplantable pulse generator may also have a unique signature that limitscommunication to only the dedicated controllers (e.g., the matchedpatient controller, implantable pulse generator charger, or a clinicianprogrammer configured for the implantable pulse generator in question).

The implantable pulse generator 18 desirably incorporates wirelesstelemetry as an element of the implantable pulse generator circuit 20shown in FIG. 6. A circuit diagram showing a desired configuration forthe wireless telemetry feature is shown in FIG. 7. It is to beappreciated that modifications to this circuit diagram configurationwhich produce the same or similar functions as described are within thescope of the invention.

As shown in FIG. 5A, the assembly 10 desirably includes a clinicianprogrammer 36 that, through a wireless telemetry 38, transfers commands,data, and programs into the implantable pulse generator 18 and retrievesdata out of the implantable pulse generator 18. In some configurations,the clinician programmer may communicate with more than one implantablepulse generator implanted in the same user.

The clinician programmer 36 may incorporate a custom programmed generalpurpose digital device, e.g., a custom program, industry standardhandheld computing platform or other personal digital assistant (PDA).The clinician programmer 36 can include an on-board microcontrollerpowered by a rechargeable battery. The rechargeable battery of theclinician programmer 36 may be recharged in the same or similar manneras described and shown for the recharger 34, i.e., docked on a chargingbase 39 (see FIG. 4C); or the custom electronics of the clinicianprogrammer may receive power from the connected PDA. The microcontrollercarries embedded code which may include pre-programmed rules oralgorithms that allow a clinician to remotely download program stimulusparameters and stimulus sequences parameters into the implantable pulsegenerator 18. The microcontroller of the clinician programmer 36 is alsodesirably able to interrogate the implantable pulse generator and uploadusage data from the implantable pulse generator. FIG. 5A shows onepossible application where the clinician is using the programmer 36 tointerrogate the implantable pulse generator. FIG. 5B shows analternative application where the clinician programmer, or a clinicianprogrammer derivative 33 intended for remote programming applicationsand having the same or similar functionality as the clinicianprogrammer, is used to interrogate the implantable pulse generator. Ascan be seen, the clinician programmer derivative 33 is connected to alocal computer, allowing for remote interrogation via a local areanetwork, wide area network, or Internet connection, for example.

Using subsets of the clinician programmer software, features of theclinician programmer 36 or clinician programmer derivative 33 mightinclude the ability of the clinician or physician to remotely monitorand adjust parameters using the Internet or other known or futuredeveloped networking schemes. A clinician programmer derivative 33 (orperhaps a feature included in the implantable pulse generator charger)would desirably connect to the patient's computer in their home throughan industry standard network such as the Universal Serial Bus (USB),where in turn an applet downloaded from the clinician's server wouldcontain the necessary code to establish a reliable transport levelconnection between the implantable pulse generator 18 and theclinician's client software, using the clinician programmer derivative33 as a bridge. Such a connection may also be established throughseparately installed software. The clinician or physician could thenview relevant diagnostic information, such as the health of the unit orits current settings, and then modify the stimulus settings in theimplantable pulse generator or direct the patient to take theappropriate action. Such a feature would save the clinician, the patientand the health care system substantial time and money by reducing thenumber of office visits during the life of the implant.

Other features of the clinician programmer, based on an industrystandard platform, might include the ability to connect to theclinician's computer system in his or hers office. Such features maytake advantage of the Conduit connection employed by Palm OS baseddevices. Such a connection then would transfer relevant patient data tothe host computer or server for electronic processing and archiving.With a feature as described here, the clinician programmer then becomesan integral link in an electronic chain that provides better patientservice by reducing the amount of paperwork that the physician's officeneeds to process on each office visit. It also improves the reliabilityof the service since it reduces the chance of mis-entered or mis-placedinformation, such as the record of the parameter setting adjusted duringthe visit.

With the use of a patient controller 37 (see FIG. 5C), the wireless link38 allows a patient to control a limited range of parameters within theimplantable pulse generator, such as operation modes/states,increase/decrease or optimize stimulus patterns, or provide open orclosed loop feedback from an external sensor or control source. Thewireless telemetry 38 also desirably allows the user to interrogate theimplantable pulse generator 18 as to the status of its internal battery22. The full ranges within these parameters may be controlled, adjusted,and limited by a clinician, so the user may not be allowed the fullrange of possible adjustments.

In one embodiment, the patient controller 37 is sized and configured tocouple to a key chain, as seen in Fig SC. It is to be appreciated thatthe patient controller 37 may take on any convenient shape, such as aring on a finger or an attachment to a belt, for example. It may also bedesirable to combine both the functions of the implantable pulsegenerator charger and the patient controller into a single externaldevice.

The recharger 34 shown in FIGS. 4A and 4B may also use wirelesstelemetry to communicate with the implantable pulse generator 18, so asto adjust the magnitude of the magnetic field 52 to allow optimalrecharging of the implantable pulse generator battery 22 whileminimizing unnecessary power consumption by the recharger and powerdissipation in the implantable pulse generator (through circuit lossesand/or through absorption by implantable pulse generator case andconstruction).

For example, a suitable, low power wireless telemetry transceiver(radio) chip set can operate in the MICS (Medical Implant CommunicationsService) band (403 MHz to 406 MHz) or other VHF/UHF low power,unlicensed bands. A wireless telemetry link not only makes the task ofcommunicating with the implantable pulse generator 18 easier, but italso makes the link suitable for use in motor control applications wherethe user issues a command to the implantable pulse generator to producemuscle contractions to achieve a functional goal (e.g., to stimulateankle flexion to aid in the gait of an individual after a stroke)without requiring a coil or other component taped or placed on the skinover the implanted implantable pulse generator.

Appropriate use of power management techniques is important to theeffective use of wireless telemetry. Desirably, the implantable pulsegenerator is exclusively the communications slave, with allcommunications initiated by the external controller (the communicationsmaster). The receiver chip of the implantable pulse generator is OFFmore than 99% of the time and is pulsed on periodically to search for acommand from an external controller, including but not limited to theimplantable pulse generator charger 34, the clinician programmer 36, andthe patient controller 37. Communications protocols include appropriatecheck and message acknowledgment handshaking to assure the necessaryaccuracy and completeness of every message. Some operations (such asreprogramming or changing stimulus parameters) require rigorous messageaccuracy testing and acknowledgement. Other operations, such as a singleuser command value in a string of many consecutive values, might requireless rigorous checking and a more loosely coupled acknowledgement.

The timing with which the implantable pulse generator enables itstransceiver to search for RF telemetry from an external controller isprecisely controlled (using a time base established by a quartz crystal)at a relatively low rate (e.g., twice per second; i.e., every 500milliseconds). This allows the external controller to time when theimplantable pulse generator responds to a command and then tosynchronize its commands with when the implantable pulse generator willbe listening for commands. This, in turn, allows commands issued withina short time (seconds to minutes) of the last command to be captured andacted upon without having to ‘broadcast’ an idle or pause signal for 500milliseconds before actually issuing the command in order to know thatthe implantable pulse generator will have enabled its receiver andreceived the command. Similarly, the communications sequence isconfigured to have the external controller issue commands insynchronization with when the implantable pulse generator will belistening for a command. Similarly, the command set implemented isselected to minimize the number of messages necessary and the length ofeach message consistent with the appropriate level of error detectionand message integrity monitoring. It is to be appreciated that themonitoring rate may vary faster or slower depending on the application,and may vary over time within a given application.

A suitable radio chip is used for the half duplex wirelesscommunications, e.g., the AMIS-52100 (AMI Semiconductor; Pocatello,Id.). This transceiver chip is designed specifically for the MICS andits European counter-part the ULP-AMI (Ultra Low Power-Active MedicalImplant) band. This chip set is optimized by micro-power operation withrapid start-up, and RF ‘1 sniffing’ circuitry.

d. Stimulus Output Stage

According to one desirable technical feature, the implantable pulsegenerator 18 desirably uses a single stimulus output stage (generator)that is directed to one or more output channels (electrode surfaces) byanalog switch(es) or analog multiplexer(s). Desirably, the implantablepulse generator 18 will deliver at least two channels of stimulation viaa lead/electrode. For applications requiring more stimulus channels,several channels (perhaps up to four) can be generated by a singleoutput stage. In turn, two or more output stages could be used, eachwith separate multiplexing to multiple channels, to allow an implantablepulse generator with eight or more stimulus channels. The stimulationdesirably has a biphasic waveform (net DC current less than 10 μA),amplitude of at least 8 mA, for neuromodulation applications, or 16 mAto 20 mA for muscle stimulation applications, and pulse durations up to500 microseconds. The stimulus current (amplitude) and pulse durationbeing programmable on a channel to channel basis and adjustable overtime based on a clinically programmed sequence or regime or based onuser (patient) commands received via the wireless communications link.

A circuit diagram showing a desired configuration for the stimulusoutput stage feature is shown in FIG. 8. It is to be appreciated thatmodifications to this circuit diagram configuration which produce thesame or similar functions as described are within the scope of theinvention.

For neuromodulation/central nervous system applications, the implantablepulse generator 18 desirably has the capability of applying stimulationtwenty-four hours per day. A typical stimulus regime for suchapplications might have a constant stimulus phase, a no stimulus phase,and ramping of stimulus levels between these phases.

Desirably, the implantable pulse generator 18 includes a single stimulusgenerator (with its associated DC current blocking output capacitor)which is multiplexed to a number of output channels; or a small numberof such stimulus generators each being multiplexed to a number of outputchannels. This circuit architecture allows multiple output channels withvery little additional circuitry. A typical, biphasic stimulus pulse isshown in FIG. 6. Note that the stimulus output stage circuitry 46 mayincorporate a mechanism to limit the recovery phase current to a smallvalue (perhaps 0.5 mA). Also note that the stimulus generator (and theassociated timing of control signals generated by the microcontroller)may provide a delay (typically of the order of 100 microseconds) betweenthe cathodic phase and the recovery phase to limit the recovery phasediminution of the cathodic phase effective at eliciting a neuralexcitation. The charge recovery phase for any electrode (cathode) mustbe long enough to assure that all of the charge delivered in thecathodic phase has been returned in the recovery phase, i.e., greaterthan or equal to five time constants are allowed for the recovery phase.This will allow the stimulus stage to be used for the next electrodewhile assuring there is no net DC current transfer to any electrode.Thus, the single stimulus generator having this characteristic would belimited to four channels (electrodes), each with a maximum frequency of30 Hz to 50 Hz. This operating frequency exceeds the needs of manyindications for which the implantable pulse generator is well suited.For applications requiring more channels (or higher composite operatingfrequencies, two or more separate output stages might each bemultiplexed to multiple (e.g., four) electrodes.

e. The Lead Connection Header

According to one desirable technical feature, the implantable pulsegenerator 18 desirably includes a lead connection header 14 forconnecting the lead(s) 12 that will enable reliable and easy replacementof the lead/electrode (see FIGS. 2A and 2B), and includes a smallantenna 54 for use with the wireless telemetry feature.

The implantable pulse generator desirably incorporates a connectionheader (top header) 14 that is easy to use, reliable, and robust enoughto allow multiple replacements of the implantable pulse generator aftermany years (e.g., more than ten years) of use. The surgical complexityof replacing an implantable pulse generator is usually low compared tothe surgical complexity of correctly placing the implantable lead12/electrode 16 in proximity to the target nerve/tissue and routing thelead 12 to the implantable pulse generator. Accordingly, the lead 12 andelectrode 16 desirably has a service life of at least ten years with aprobable service life of fifteen years or more. Based on the clinicalapplication, the implantable pulse generator may not have this long aservice life. The implantable pulse generator service life is largelydetermined by the number of charge-discharge cycles of the Lithium Ionbattery 22, and is likely to be three to ten years, based on the usageof the device. Most desirably, the implantable pulse generator 18 has aservice life of at least five years.

As described above, the implantable pulse generator preferably will usea laser welded titanium case. As with other active implantable medicaldevices using this construction, the implantable lead(s) 12 connect tothe implantable pulse generator through a molded or cast polymericconnection header 14 (top header). Metal-ceramic or metal-glassfeed-thrus maintain the hermetic seal of the titanium capsule whileproviding electrical contact to the electrical contact(s) of the lead12/electrode 16.

The standard implantable connectors may be similar in design andconstruction to the low-profile IS-1 connector system (per ISO 5841-3).The IS-1 connectors have been in use since the late 1980s and have beenshown to be reliable and provide easy release and re-connection overseveral implantable pulse generator replacements during the service lifeof a single pacing lead. Full compatibility with the IS-1 standard, andmating with pacemaker leads, is not a requirement for the implantablepulse generator.

The implantable pulse generator connection system may include amodification of the IS-1 connector system, which shrinks the axiallength dimensions while keeping the format and radial dimensions of theIS-1. For application with more than two electrode conductors, the topheader 14 may incorporate one or more connection receptacles each ofwhich accommodate leads with typically four conductors. When two or moreleads are accommodated by the header, these lead may exit the connectionheader in opposite directions (i.e., from opposite sides of the header)

These connectors can be similar to the banded axial connectors used byother multi-polar implantable pulse generators or may follow theguidance of the draft IS-4 implantable connector standard. The design ofthe implantable pulse generator housing and header 14 preferablyincludes provisions for adding the additional feed-thrus and largerheaders for such indications.

The inclusion of the UHF antenna 54 for the wireless telemetry insidethe connection header (top header) 14 is necessary as the shieldingoffered by the titanium case will severely limit (effectively eliminate)radio wave propagation through the case. The antenna 54 connection willbe made through a feed-thru similar to that used for the electrodeconnections. Alternatively, the wireless telemetry signal may be coupledinside the implantable pulse generator onto a stimulus output channeland coupled to the antenna 54 with passive filtering/couplingelements/methods in the connection header 14.

f. The Microcontroller

According to one desirable technical feature, the implantable pulsegenerator 18 desirably uses a standard, commercially availablemicro-power, flash programmable microcontroller 24 or processor core inan application specific integrated circuit (ASIC). This device (orpossibly more than one such device for a computationally complexapplication with sensor input processing) and other large semiconductorcomponents may have custom packaging such as chip-on-board, solder flipchip, or adhesive flip chip to reduce circuit board real estate needs.

A circuit diagram showing a desired configuration for themicrocontroller 24 is shown in FIG. 12. It is to be appreciated thatmodifications to this circuit diagram configuration which produce thesame or similar functions as described are within the scope of theinvention.

g. Power Management Circuitry

According to one desirable technical feature, the implantable pulsegenerator 18 desirably includes efficient power management circuitry asan element of the implantable pulse generator circuitry 20 shown in FIG.6. The power management circuitry is generally responsible for theefficient distribution of power, the recovery of power from the RFmagnetic field 52, and for charging and monitoring the Lithium Ionbattery 22. In addition, the operation of the implantable pulsegenerator 18 can be described in terms of having operating modes asrelating to the function of the power management circuitry. These modesmay include, but are not limited to IPG Active and Charging, IPG Active,and IPG Dormant. These modes will be described below in terms of theprinciples of operation of the power management circuitry using possiblecircuit diagrams shown in FIGS. 11 and 12. FIG. 11 shows one possiblepower management sub-circuit having MOSFET isolation between the battery22 and the charger circuit. FIG. 12 shows another possible powermanagement sub-circuit diagram without having MOSFET isolation betweenthe battery 22 and the charger circuit. In the circuit without theisolation MOSFET (see FIG. 12), the leakage current of the disabledcharge control integrated circuit chip (U1) must be very low to preventthis leakage current from discharging the battery 22 in all modes(including the Dormant Mode). Except as noted, the description of thesemodes applies to both circuits.

i. IPG Active and Charging Mode

The IPG Active and Charging mode occurs when the implantable pulsegenerator 18 is being charged. In this mode, the implantable pulsegenerator is active, i.e., the microcontroller 24 is powered andcoordinating wireless communications and may be timing and controllingthe generation and delivery of stimulus pulses. The implantable pulsegenerator 18 may be communicating with the implantable pulse generatorcharger 34 concerning the magnitude of the battery voltage and the DCvoltage recovered from the RF magnetic field 52. The charger 34 usesthis data for two purposes: to provide feedback to the user about theproximity of the charging coil 35 to the implanted pulse generator, andto increase or decrease the strength of the RF magnetic field 52. This,in turn, minimizes the power losses and undesirable heating of theimplantable pulse generator.

While in the IPG Active and Charging mode, the power managementcircuitry 40 serves the following primary functions:

(1) provides battery power to the rest of the implantable pulsegenerator circuitry,

(2) recovers power from the RF magnetic field 52 generated by theimplantable pulse generator charger 34,

(3) provides controlled charging current (from the recovered power) tothe battery 22, and

(4) communicates with the implantable pulse generator charger 34 via thewireless telemetry link 38 to provide feedback to the user positioningthe charging coil 35 over the implantable pulse generator, and to causethe implantable pulse generator charger 34 to increase or decrease thestrength of its RF magnetic field 52 for optimal charging of theimplantable pulse generator battery 22 (Lithium Ion battery).

i(a) Principles of Operation, IPG Active and Charging Mode

-   -   i(a) (1) RF voltage is induced in the Receive Coil by the RF        magnetic field 52 of the implantable pulse generator charger 34    -   i(a) (2) Capacitor C1 is in series with the Receive Coil and is        selected to introduce a capacitive reactance that compensates        (subtracts) the inductive reactance of the Receive Coil    -   i(a) (3) D1-D2 form a full wave rectifier that converts the AC        voltage recovered by the Receive Coil into a pulsating DC        current flow    -   i(a) (4) This pulsating DC current is smoothed (filtered) by C3        (this filtered DC voltage is labeled VRAW)    -   i(a) (5) D4 is a zener diode that acts as a voltage limiting        device (in normal operation, D4 is not conducting significant        current)    -   i(a) (6) D3 prevents the flow of current from the battery 22        from preventing the correct operation of the Charge Management        Circuitry once the voltage recovered from the RF magnetic field        is removed. Specifically, current flow from the battery (through        Q3 (turned ON), in the case for the circuit of FIG. 11) through        the body diode of Q2 would hold ON the charge controller IC        (U1). This additional current drain would be present in all        modes, including dormant, and would seriously limit battery        operating life. Additionally, this battery current pathway would        keep Q6 turned ON even if the magnetic reed switch (S1) were        closed; thus preventing the isolation of the IPG circuitry from        the battery in the dormant mode. In FIG. 11, D3 is desirably a        schottky diode because of the lower forward voltage drop;        whereas it is desirably a conventional silicone diode in FIG. 12        because of the lower reverse voltage leakage current.    -   i(a) (7) U1, Q2, R2, C4, C6, and C2 form the battery charger        sub-circuit        -   U1 is a micropower, Lithium Ion Charge Management Controller            chip implementing a constant current phase and constant            voltage phase charge regime. This chip desirably            incorporates an internal voltage reference of high accuracy            (±0.5%) to establish the constant voltage charge level. U1            performs the following functions:        -   monitors the voltage drop across a series resistor R2            (effectively the current charging the battery 22) to control            the current delivered to the battery through the external            pass transistor Q2. U1 uses this voltage across R2 to            establish the current of the constant current phase            (typically the battery capacity divided by five hours), and        -   decreases the current charging the battery as required to            limit the battery voltage and effectively transition from            constant current phase to constant voltage phase as the            battery voltage approaches the terminal voltage,    -   i(a) (8) U1 also includes provisions for timing the duration of        the constant current and constant voltage phases and suspends        the application of current to the battery 22 if too much time is        spent in the phase. These fault timing features of U1 are not        used in normal operation.    -   i(a) (9) In this circuit, the constant voltage phase of the        battery charging sequence is timed by the microcontroller 24 and        not by U1. The microcontroller monitors the battery voltage and        terminates the charging sequence (i.e., tells the implantable        pulse generator charger 34 that the implantable pulse generator        battery 22 is fully charged) after the battery voltage has been        in the constant voltage region for greater than a fixed time        period (e.g., 15 to 20 minutes).    -   i(a) (10) In FIG. 11, Q3 and Q5 are turned ON only when the        charging power is present. This effectively isolates the        charging circuit from the battery 22 when the externally        supplied RF magnetic field 52 is not present and providing power        to charge the battery.    -   i(a) (11) In FIG. 12, U1 is always connected to the battery 22,        and the disabled current of this chip is a load on the battery        22 in all modes (including the dormant mode). This, in turn, is        a more demanding requirement on the current consumed by U1 while        disabled.    -   i(a) (12) F1 is a fuse that protects against long-duration, high        current component failures. In all anticipated transient high        current failures, (i.e., soft failures that cause the circuitry        to consume high current levels and thus dissipate high power        levels; but the failure initiating the high current flow is not        permanent and the circuit will resume normal function if the        circuit is removed from the power source before damage from        overheating occurs), the VBAT circuitry will disconnect the        battery 22 from the temporary high load without blowing the        fuse. The specific sequence is:        -   -   High current flows into a component(s) powered by VBAT                (most likely the VHH power supply or an element powered                by the VCC power supply).            -   The voltage drop across the fuse will (prior to the fuse                blowing) turn ON Q1 (based on the current flow through                the fuse causing a 0.5V to 0.6V drop across the                resistance of F1).            -   The collector current from Q1 will turn off Q4.            -   VBAT drops very quickly and, as a direct result, VCC                falls. In turn, the voltage on the PortD4 IO pin from                the microcontroller voltage falls as VCC falls, through                the parasitic diodes in the microcontroller 24. This                then pulls down the voltage across C6 as it is                discharged through R12.            -   The implantable pulse generator is now stable in the                Dormant Mode, i.e., VBAT is disconnected from the                battery 22 by a turned OFF Q4. The only load remaining                on the battery is presented by the charging circuit and                by the analog multiplexer (switches) U3 that are used to                direct an analog voltage to the microcontroller 24 for                monitoring the battery voltage and (by subtracting the                voltage after the resistance of F1) an estimate of the                current consumption of the entire circuit. A failure of                these voltage monitoring circuits is not protected by                the fuse, but resistance values limit the current flow                to safe levels even in the event of component failures.                A possible source of a transient high-current circuit                failure is the SCR latchup or supply-to-ground short                failure of a semiconductor device directly connected to                VBAT or VCC.    -   i(a) (13) R9 & R11 form a voltage divider to convert VRAW        (approximately zero volts to eight volts) into the voltage range        of the microcontroller's A-D inputs (used for closed loop        control of the RF magnetic field strength),    -   i(a) (14) R8 and C9 form the usual R-C reset input circuit for        the microcontroller 24; this circuit causes a hardware reset        when the magnetic reed switch (S1) is closed by the application        of a suitable static magnetic field for a short duration,    -   i(a) (15) R10 and C8 form a much slower time constant that        allows the closure of the reed switch by the application of the        static magnetic field for a long duration to force the        implantable pulse generator into the Dormant mode by turning OFF        Q6 and thus turning OFF Q4. The use of the magnetic reed switch        for resetting the microcontroller 24 or forcing a total        implantable pulse generator shutdown (Dormant mode) may be a        desirable safety feature.

ii. IPG Active Mode

The IPG Active mode occurs when the implantable pulse generator 18 isnot being charged and it is operating normally. In this mode, theimplantable pulse generator may be generating stimulus outputs or it maybe waiting for the next request to generate stimulus in response to atimed neuromodulation sequence or a telemetry command from an externalcontroller. In this mode, the implantable pulse generator is active(microcontroller 24 is powered and coordinating wireless communicationsand may be timing & controlling the generation and delivery of stimuluspulses). There is no implantable pulse generator charger 34 present.

ii(a) Principles of Operation, IPG Active Mode

In the IPG Active mode, there is no implantable pulse generator charger34 present, and thus no DC voltage recovered by Receive Coil, D1, D2,and C3. In FIG. 11, the lack of DC current from VRAW means that Q5 isheld off. This, in turn, holds Q3 off and the charging circuitry isisolated from the battery 22. In FIG. 12, the lack of DC current fromVRAW means that U1 is disabled. This, in turn, keeps the current drainfrom the battery 22 to an acceptably low level, typically less than 1μA.

iii. IPG Dormant Mode

The IPG Dormant mode occurs when the implantable pulse generator 18 isnot being charged and it is completely disabled (powered down). In thismode, power is not being supplied to the microcontroller 24 or otherenabled circuitry. This is the mode for the long-term storage of theimplantable pulse generator before or after implantation. The dormantmode may only be exited by placing the implantable pulse generator intothe Active and Charging mode by placing the implantable pulse generatorcharging coil 35 of a functional implantable pulse generator charger 34in close proximity to the implantable pulse generator 18.

iii(a) Principles of Operation, IPG Dormant Mode

In the IPG Dormant mode, there is no implantable pulse generator charger34 present, and thus no DC voltage recovered by Receive Coil, D1, D2,and C3. VBAT is not delivered to the remainder of the implantable pulsegenerator circuitry because Q4 is turned off. The Dormant mode is stablebecause the lack of VBAT means that VCC is also not present, and thus Q6is not held on through R8 and R10. Thus the battery 22 is completelyisolated from all load circuitry (the VCC power supply and the VHH powersupply).

The Dormant mode is entered through the application of a long magnetplacement over S1 (magnetic reed switch) or through the reception of acommand by the wireless telemetry. In the case of the telemetry command,the PortD4, which is normally configured as a microcontroller input, isconfigured as a logic output with a logic low (0) value. This, in turn,discharges C8 through R12 and turns off Q6; which, in turn, turns off Q4and forces the implantable pulse generator into the Dormant mode. Notethat R12 is much smaller in value than R10, thus the microcontroller 24can force C8 to discharge even though VCC is still present.

In FIG. 11, the lack of DC current from VRAW means that Q5 is held off.This, in turn, holds Q3 off and the charging circuitry is isolated fromthe battery 22. Also, Q4 was turned off. In FIG. 12, the lack of DCcurrent from VRAW means that U1 is disabled. This, in turn, keeps thecurrent drain from the battery 22 to an acceptably low level, typicallyless than 1 μA.

2. Representative Implantable Pulse Generator Circuitry

FIG. 6 shows a representative circuit 20 for the implantable pulsegenerator 18 that takes into account the desirable technical featuresdiscussed above.

The circuit 20 can be grouped into functional blocks, which generallycorrespond to the association and interconnection of the electroniccomponents. FIG. 6 shows a block diagram that provides an overview of arepresentative desirable implantable pulse generator design.

In FIG. 6, seven functional blocks are shown: (1) The Microprocessor orMicrocontroller 24; (2) the Power Management Circuit 40 for the battery22; (3) the VCC Power Supply 42; (4) the VHH Power Supply 44; (5) theStimulus Output Stage(s) 46; (6) the Output Multiplexer(s) 48; and (7)the Wireless Telemetry Circuit 50.

For each of these blocks, the associated functions, possible keycomponents, and circuit description are now described.

a. The Microcontroller

The Microcontroller 24 is generally responsible for the followingfunctions:

(1) The timing and sequencing of the stimulator stage and the VHH powersupply used by the stimulator stage,

(2) The sequencing and timing of power management functions,

(3) The monitoring of the battery voltage, the voltage recovered fromthe RF magnetic field 52 during the battery charging process, thestimulator voltages produced during the generation of stimulus pulses,and the total circuit current consumption, VHH, and VCC,

(4) The timing, control, and interpretation of commands to and from thewireless telemetry circuit,

(5) The logging (recording) of patient usage data as well as clinicianprogrammed stimulus parameters and configuration data, and

(6) The processing of commands (data) received from the user (patient)via the wireless link to modify the characteristics of the stimulusbeing delivered.

The use of a microcontroller incorporating flash programmable memoryallows the operating program of the implantable pulse generator as wellas the stimulus parameters and settings to be stored in non-volatilememory (data remains safely stored even if the battery 22 becomes fullydischarged, or if the implantable pulse generator is placed in theDormant Mode). Yet, the data (operating program, stimulus parameters,usage history log, etc.) can be erased and reprogrammed thousands oftimes during the life of the implantable pulse generator. The software(firmware) of the implantable pulse generator must be segmented tosupport the operation of the wireless telemetry routines while the flashmemory of the microcontroller 24 is being erased and reprogrammed.Similarly, the VCC power supply 42 must support the power requirementsof the microcontroller 24 during the flash memory erase and programoperations.

Although the microcontroller 24 may be a single component, the firmwareis developed as a number of separate modules that deal with specificneeds and hardware peripherals. The functions and routines of thesesoftware modules are executed sequentially; but the execution of thesemodules are timed and coordinated so as to effectively functionsimultaneously. The microcontroller operations that are associateddirectly with a given hardware functional block are described with thatblock.

The Components of the Microcontroller Circuit may include:

(1) A single chip microcontroller 24. This component may be a member ofthe Texas Instruments MSP430 family of flash programmable, micro-power,highly integrated mixed signal microcontroller. Likely family members tobe used include the MSP430F1610, MSP430F1611, MSP430F1612, MSP430F168,and the MSP430F169. Each of these parts has numerous internalperipherals, and a micropower internal organization that allows unusedperipherals to be configured by minimal power dissipation, and aninstruction set that supports bursts of operation separated by intervalsof sleep where the microcontroller suspends most functions.

(2) A miniature, quartz crystal (X1) for establishing precise timing ofthe microcontroller. This may be a 32.768 KHz quartz crystal.

(3) Miscellaneous power decoupling and analog signal filteringcapacitors.

b. Power Management Circuit

The Power Management Circuit 40 (and associated microcontroller actions)is generally responsible for the following functions:

(1) recover power from the Receive Coil,

(2) control delivery of the Receive Coil power to recharge the LithiumIon secondary battery 22,

(3) monitor the battery voltage during charge and discharge conditions,

(4) communicate (through the wireless telemetry link 38) with theexternally mounted implantable pulse generator charger 34 to increase ordecrease the strength of the RF magnetic field 52 for optimal chargingof the battery,

(5) suspend stimulation when the battery voltage becomes very low,and/or suspend all operation (go into the Dormant Mode) when the batteryvoltage becomes critically low,

(6) disable (with single fault tolerance) the delivery of chargingcurrent to the battery 22 in overcharge conditions,

(7) communicate (through the wireless telemetry link 38 ) with theexternal equipment the charge status of the battery 22,

(8) prevent (with single fault tolerance) the delivery of excessivecurrent from the battery 22,

(9) provide battery power to the rest of the circuitry of theimplantable pulse generator, i.e., VCC and VHH power supplies,

(10) provide isolation of the Lithium Ion battery 22 from othercircuitry while in the Dormant Mode,

(11) provide a hard microprocessor reset and force entry into theDormant Mode in the presence of a pacemaker magnet (or comparabledevice), and

(12) provide the microcontroller 24 with analog voltages with which tomeasure the magnitude of the recovered power from the RF magnetic field52, the battery voltage, and the appropriate battery current flow (drainand charge).

The Components of the Power Management Circuit may include:

(1) The Receive Coil, which desirably comprises a multi-turn, finecopper wire coil near the inside perimeter of the implantable pulsegenerator 18. Preferably, the receive coil includes a predeterminedconstruction, e.g., desirably 250 to 350 turns, and more desirably 300turns of four strands of #40 enameled magnetic wire, or the like. Themaximizing of the coil's diameter and reduction of its effective RFresistance allows necessary power transfer at and beyond the typicalimplant depth of about one centimeter.

(2) A micropower Lithium Ion battery charge management controller IC(integrated circuit); such as the MicroChip MCP73843-41, or the like.

(3) Low on resistance, low threshold P channel MOSFETs with very low offstate leakage current (Q2, Q3, and Q4).

(4) Analog switches (or an analog multiplexer) U3.

(5) Logic translation N-channel MOSFETs (Q5 & Q6) with very low offstate leakage current.

c. The VCC Power Supply

The VCC Power Supply 42 is generally responsible for the followingfunctions:

(1) Provide the microcontroller 24 and other circuitry with regulated3.3 VDC (typical) despite changes in the Lithium Ion battery voltage.Other useable voltages include 3.0 VDC, 2.7 VDC, and the like.

The Components of the VCC Power Supply might include:

(1) Micropower, low drop out, linear voltage regulator; e.g., MicrochipNCP1700T-3302, Maxim Semiconductor MAX1725, or Texas InstrumentsTPS79730, or the like.

The characteristics of the VCC Power Supply might include:

(1) quiescent current, i.e., the current wasted by the power supply inits normal operation. This value should be less than a few microamperes,and

(2) drop-out voltage, i.e., the minimal difference between the VBATsupplied to the VCC power supply and its output voltage. This voltagemay be less than about 100 mV even at the current loads presented by thetransmitter of the wireless telemetry circuitry.

d. VHH Power Supply

A circuit diagram showing a desired configuration for the VHH powersupply 44 is shown in FIG. 13. It is to be appreciated thatmodifications to this circuit diagram configuration which produce thesame or similar functions as described are within the scope of theinvention.

The VHH Power Supply 44 is generally responsible for the followingfunctions:

(1) Provide the Stimulus Output Stage 46 and the Output Multiplexer 48with a programmable DC voltage between the battery voltage and a voltagehigh enough to drive the required cathodic phase current through theelectrode circuit plus the voltage drops across the stimulator stage,the output multiplexer stage, and the output coupling capacitor. VHH istypically 12 VDC or less for neuromodulation applications; and 25V orless for muscle stimulation applications.

The Components of the VHH Power Supply might include:

(1) Micropower, inductor based (fly-back topology) switch mode powersupply (U10); e.g., Texas Instruments TPS61045, Texas InstrumentsTPS61041, or Linear Technology LT3464 with external voltage adjustmentcomponents.

(2) L6 is the flyback energy storage inductor.

(3) C42 & C43 form the output capacitor.

(4) R27, R28, and R29 establish the operating voltage range for VHHgiven the internal DAC which is programmed via the SETVHH logic commandfrom the microcontroller 24.

(5) Diode D9 serves no purpose in normal operation and is added to offerprotection from over-voltage in the event of a VHH circuit failure.

(6) The microcontroller 24 monitors VHH for detection of a VHH powersupply failure, system failures, and optimizing VHH for the exhibitedelectrode circuit impedance.

e. Stimulus Output Stage

The Stimulus Output Stage(s) 46 is generally responsible for thefollowing functions:

(1) Generate the identified biphasic stimulus current with programmable(dynamically adjustable during use) cathodic phase amplitude, pulsewidth, and frequency. The recovery phase may incorporate a maximumcurrent limit; and there may be a delay time (most likely a fixed delay)between the cathodic phase and the recovery phase (see FIG. 9). Typicalcurrents (cathodic phase) for neuromodulation applications are 1 mA to10 mA; and 2 mA to 20 mA for muscle stimulation applications. Forapplications using nerve cuff electrodes or other electrodes that are invery close proximity to the excitable neural tissue, stimulus amplitudesof less than 1 mA may be provided. Electrode circuit impedances can varywith the electrode and the application, but are likely to be less than2,000 ohms and greater than 100 ohms across a range of electrode types.

The Components of the Stimulus Output Stage (as represented in FIG. 8)may include:

(1) The cathodic phase current through the electrode circuit isestablished by a high gain (HFE) NPN transistor (Q7) with emitterdegeneration. In this configuration, the collector current of thetransistor (Q7) is defined by the base drive voltage and the value ofthe emitter resistor (R24).

Two separate configurations are possible: In the first configuration (asshown in FIG. 8), the base drive voltage is provided by a DAC peripheralinside the microcontroller 24 and is switched on and off by a timerperipheral inside the microcontroller. This switching function isperformed by an analog switch (U8). In this configuration, the emitterresistor (R24) is fixed in value and fixed to ground.

In a second alternative configuration, the base drive voltage is a fixedvoltage pulse (e.g., a logic level pulse) and the emitter resistor ismanipulated under microcontroller control. Typical options may includeresistor(s) terminated by microcontroller IO port pins that are held orpulsed low, high, or floating; or an external MOSFET that pulls one ormore resistors from the emitter to ground under program control. Notethat the pulse timing need only be applied to the base drive logic; thetiming of the emitter resistor manipulation is not critical.

The transistor (Q7) desirably is suitable for operation with VHH on thecollector. The cathodic phase current through the electrode circuit isestablished by the voltage drop across the emitter resistor. Diode D7,if used, provides a degree of temperature compensation to this circuit.

(2) The microcontroller 24 (preferably including a programmablecounter/timer peripheral) generates stimulus pulse timing to generatethe cathodic and recovery phases and the interphase delay. Themicrocontroller 24 also monitors the cathode voltage to confirm thecorrect operation of the output coupling capacitor, to detect systemfailures, and to optimize VHH for the exhibited electrode circuitimpedance; i.e., to measure the electrode circuit impedance.Additionally, the microcontroller 24 can also monitor the pulsingvoltage on the emitter resistor; this allows the fine adjustment of lowstimulus currents (cathodic phase amplitude) through changes to the DACvalue.

f. The Output Multiplexer

The Output Multiplexer 48 is generally responsible for the followingfunctions:

(1) Route the Anode and Cathode connections of the Stimulus Output Stage46 to the appropriate electrode based on addressing data provided by themicrocontroller 24.

(2) Allow recharge (recovery phase) current to flow from the outputcoupling capacitor back through the electrode circuit with aprogrammable delay between the end of the cathodic phase and thebeginning of the recovery phase (the interphase delay).

The circuit shown in FIG. 8 may be configured to provide monopolarstimulation (using the case 26 as the return electrode) to Electrode 1,to Electrode 2, or to both through time multiplexing. This circuit couldalso be configured as a single bipolar output channel by changing thehardwire connection between the circuit board and the electrode; i.e.,by routing the CASE connection to Electrode 1 or Electrode 2. The use offour or more channels per multiplexer stage (i.e., per output couplingcapacitor) is likely.

The Components of the Output Multiplexer might include:

(1) An output coupling capacitor in series with the electrode circuit.This capacitor is desirably located such that there is no DC across thecapacitor in steady state. This capacitor is typically charged by thecurrent flow during the cathodic phase to a voltage range of about ¼thto 1/10th of the voltage across the electrode circuit during thecathodic phase. Similarly, this capacitor is desirably located in thecircuit such that the analog switches do not experience voltages beyondtheir ground of power supply (VHH).

(2) The analog switches (U7) must have a suitably high operatingvoltage, low ON resistance, and very low quiescent current consumptionwhile being driven from the specified logic levels. Suitable analogswitches include the Vishay/Siliconix DG412HS, for example.

(3) Microcontroller 24 selects the electrode connections to carry thestimulus current (and time the interphase delay) via address lines.

(4) Other analog switches (U9) may be used to sample the voltage of VHH,the CASE, and the selected Electrode. The switched voltage, after thevoltage divider formed by R25 and R26, is monitored by themicrocontroller 24.

g. Wireless Telemetry Circuit

The Wireless Telemetry circuit 50 is generally responsible for thefollowing functions:

(1) Provide reliable, bidirectional communications (half duplex) with anexternal controller, programmer, or charger 34, for example, via aVHF-UHF RF link (likely in the 403 MHZ to 406 MHz MICS band per FCC 47CFR Part 95 and the Ultra Low Power—Active Medical Implant (AMI)regulations of the European Union). This circuit will look for RFcommands at precisely timed intervals (e.g., twice a second), and thisfunction must consume very little power. Much less frequently thiscircuit will transmit to the external controller. This function shouldalso be as low power as possible; but will represent a lower totalenergy demand than the receiver in most of the anticipated applications.The RF carrier is amplitude modulated (on-off keyed) with the digitaldata. Serial data is generated by the microcontroller 24 alreadyformatted and timed. The wireless telemetry circuit 50 converts theserial data stream into a pulsing carrier signal during the transitprocess; and it converts a varying RF signal strength into a serial datastream during the receive process.

The Components of the Wireless Telemetry Circuit (as represented in FIG.7) might include:

(1) a crystal controlled, micropower transceiver chip such as the AMISemiconductor AMIS-52100 (U6). This chip is responsible for generatingthe RF carrier during transmissions and for amplifying, receiving, anddetecting (converting to a logic level) the received RF signals. Thetransceiver chip must also be capable of quickly starting and stoppingoperation to minimize power consumption by keeping the chip disabled(and consuming very little power) the majority of the time; and poweringup for only as long as required for the transmitting or receivingpurpose.

(2) The transceiver chip has separate transmit and receive ports thatmust be switched to a single antenna/feedthru. This function isperformed by the transmit/receive switch (US) under microcontrollercontrol via the logic line XMIT. The microcontroller 24 controls theoperation of the transceiver chip via an I²C serial communications link.The serial data to and from the transceiver chip may be handled by aUART or a SPI peripheral of the microcontroller. The messageencoding/decoding and error detection may be performed by a separate,dedicated microcontroller; else this processing will be time shared withthe other tasks of the only microcontroller.

The various inductor and capacitor components (U6) surrounding thetransceiver chip and the transmit/receive switch (US) are impedancematching components and harmonic filtering components, except asfollows:

(1) X2, C33 and C34 are used to generate the crystal controlled carrier,desirably tuned to the carrier frequency divided by thirty-two,

(2) L4 and C27 form the tuned elements of a VCO (voltage controlledoscillator) operating at twice the carrier frequency, and

(3) R20, C29, and C30 are filter components of the PLL (phase lockedloop) filter.

II. Representative Indications

Due to its technical features, the implantable pulse generator 18 asjust generally described can be used to provide beneficial results indiverse therapeutic and functional restorations indications.

For example, in the field of urology, possible indications for use ofthe implantable pulse generator 18 include the treatment of (i) urinaryand fecal incontinence; (ii) micturition/retention; (iii) restoration ofsexual function; (iv) defecation/constipation; (v) pelvic floor muscleactivity; and/or (vi) pelvic pain.

The implantable pulse generator 18 can be used for deep brainstimulation in the treatment of (i) Parkinson's disease; (ii) multiplesclerosis; (iii) essential tremor; (iv) depression; (v) eatingdisorders; (vi) epilepsy; and/or (vii) minimally conscious state.

The implantable pulse generator 18 can be used for pain management byinterfering with or blocking pain signals from reaching the brain, inthe treatment of, e.g., (i) peripheral neuropathy; and/or (ii) cancer.

The implantable pulse generator 18 can be used for vagal nervestimulation for control of epilepsy, depression, or othermood/psychiatric disorders.

The implantable pulse generator 18 can be used for the treatment ofobstructive sleep apnea.

The implantable pulse generator 18 can be used for gastric stimulationto prevent reflux or to reduce appetite or food consumption.

The implantable pulse generator 18 can be used in functionalrestorations indications such as the restoration of motor control, torestore (i) impaired gait after stroke or spinal cord injury (SCI); (ii)impaired hand and arm function after stroke or SCI; (iii) respiratorydisorders; (iv) swallowing disorders; (v) sleep apnea; and/or (vi)neurotherapeutics, allowing individuals with neurological deficits, suchas stroke survivors or those with multiple sclerosis, to recoverfunctionally.

The foregoing is considered as illustrative only of the principles ofthe invention. Furthermore, since numerous modifications and changeswill readily occur to those skilled in the art, it is not desired tolimit the invention to the exact construction and operation shown anddescribed. While the preferred embodiment has been described, thedetails may be changed without departing from the invention, which isdefined by the claims.

1. A neuromuscular stimulation system comprising: at least oneelectrically conductive surface sized and configured for implantation ina targeted neural or muscular tissue region, a lead electrically coupledto the electrically conductive surface, the lead sized and configured tobe positioned subcutaneous a tissue surface, an implantable pulsegenerator sized and configured to be coupled to the lead and positionedin subcutaneous tissue remote from the at least one electricallyconductive surface, the implantable pulse generator comprising a firstnon-inductive wireless telemetry circuitry using VHF/UHF signals, thefirst non-inductive wireless telemetry circuitry being functional at adistance as far as arm's reach away from the patient, and being adaptedfor programming and interrogation of the implantable pulse generator,and the implantable pulse generator comprising at least three powermanagement operating modes including an active mode, an idle mode, and adormant mode.
 2. A system according to claim 1 wherein the implantablepulse generator includes a smaller end and a larger end to facilitateplacement within a subcutaneous pocket small end first.
 3. A systemaccording to claim 1 wherein the implantable pulse generator includes aconnection header coupled to the first wireless telemetry circuitry, theconnection header being sized and configured to accept an IS-1 plug-inlead connector.
 4. A system according to claim 1 further including arechargeable power source and a power receiving coil coupled to therechargeable power source and carried entirely within the implantablepulse generator, the power receiving coil being configured, after thepulse generator is implanted in subcutaneous tissue, to transferreceived power from a transcutaneously applied radio frequency magneticfield to the rechargeable power source and recharge the power source ina time period of not more than six hours.
 5. A system according to claim4 wherein recharging of the rechargeable power source is required lessthan weekly.
 6. A system according to claim 1 wherein the implantablepulse generator is sized and configured for implanting in subcutaneoustissue at an implant depth of between about 0.5 cm and about 1.5 cm. 7.A system according to claim 1 wherein the rechargeable power sourcecomprises a capacity of at least 30 mA-hr.
 8. A method of using thesystem defined in claim 1.